Furnace blows but does not heat (intermittent problem)

We have a "York Diamond 90" gas-fired furnace that was working well
until today.
There seems to be something wrong with the gas flow/valve, burner, or
sensor.
I can see the electronic ignition element turning white hot, then hear
the gas valve click on, then see the blue gas flames light for a
second or two before sputtering out. This cycle repeats itself several
times until, the system "gives up" (or I guess locks out) at which
point the blower just continues to blow cold air forever and no
further ignition attempts are made. The blower continues to blow even
if I shut off the thermostat
Interestingly, if I cycle off the power (even just for a second or
two), the furnace will start up normally and ignite the burners
properly. The burner will continue to fire for a *couple of minutes*
before blowing out at which point it goes into the (failed) cycle of
trying to relight a couple of times before finally giving up and again
leaving me in the stuck state with the blower blowing cold air.
Sometimes in the cycle of trying to re-light it will burn for a
few seconds before sputtering out. Also, sometimes, I hear the valve
clicking on-and-off a couple of times in rapid succession.
Now the other two gas furnaces are working properly, so I don't think
it is a supply problem. Also, I don't think it is a ventillation problem
because it seems to burn fine for a few minutes with a nice blue flame
before suddenly sputtering out.
When I opened up the bottem panel (overriding the disable switch), I
noticed that after it locked up in the continuous blower position, the
diagnostic LED exhibited a pattern of 8 short (red) flashes -- I believe
this simply indicates that the flame is lost 5 times within a heating
cycle which according to the online manual indicates either:
Low gas pressure (unlikely since other two gas
furnaces in the house work fine, right?)
Faulty gas valve
Dirty or faulty flame sensor
Faulty hot surface igniter (unlikely because the flame does
ignite, right?)
Burner problem
Any idea what might be wrong and how to fix?
Even if this is not a DIY fix, I would like to have some idea of what
the potential problems could be so that I can intelligently engage the
service person and make sure that I am not being taken :)
Thanks!

Would this be consistent with the fact that initially the flame burns
for a couple of minutes before shutting off?
Also, if it is a flame sensor, how difficult/advisable is it as a DIY
repair? (I am very experienced in electrical, electronics & mechanical,
reasonably experienced in plumbing, but have minimal experience in gas).

Minutes? I thought you said "a second or two."
It's entirely consistent with "a second or two" multiple times over
a span of minutes.

I've never seen your particular furnace. It might just be dirty.
Look for a little gadget with a window facing the flame and a couple
of wires coming out of it. Make sure the window isn't sooty and the
wires are still connected to the control board. Judge for yourself
how hard it would be to change it.
Of course, it could also be the associated control board electronics.
Less likely, IMHO, but possible.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.

It initially burns for maybe 2-3 minutes without interruption. Then it
starts cycling with each subsequent flame lasting typically for 1-2
seconds or often even less (though sometimes I have seen it last as
long as 10 seconds).

Hi,
Flame sensor is like a keavy needle which is usually located opposite
side of ignitor. They does not go bad easily, but surface rust make them
sluggish. Use ememry cloth or fine fine snad paper to remove rust.
Most likely it'll work again,

I just went through exactly the same thing with an Amana furnace here.
It was the flame sensor and cleaning it with emory paper did the trick.
It would go into lock out and then the fan would remain on until I
reset the system.
Tony Hwang wrote:

I just went through exactly the same thing with an Amana furnace here.
It was the flame sensor and cleaning it with emory paper did the trick.
It would go into lock out and then the fan would remain on until I
reset the system.
Tony Hwang wrote:

One interesting additional (but probably unrelated fact)...
The only recent change to the system is that two days ago I installed
a condensate pump since previously all the condensate was just
dripping vertically down a 2-story 3/4" pvc pipe onto our crawl space
floor. I connected a short length of 5/8" clear flexible tube to the
end of the pvc pipe which then hangs over the basin of the condensate
pump. The condensate pump seems to be pumping the water fine.
Not sure how this could be related to my problem since the water is
draining by gravity into a basically open reservoir so I don't see how
it can be backed up two stories to the height of the furnace. However,
the timing is strangely coincidental...

Why exactly is it that you homemoaners think you need to "engage" the
service tech? All that does is run your bill up while we waste time
chit chatting on your dime. A good tech really doesnt need to hear a
word from you other than, "the heat doesnt work and its down there in
the basement". If he needs any more than that then he isnt much of a
competent tech.
If you want to fix it yourself, pull all the parts off the working
furnace and start putting them on the inoperative furnace one by one
till you get it. Whats the worst that can happen?
Your burn yourself, you asphyxiate yourself or your family, you burn
your house down or you electrocute yourself.
and maybe, just maybe, you might get it right.
Bubba

Log in

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.